The H2S Problem

The transport of sewage to a municipality’s waste water treatment plant involves sections of downhill and uphill flows.  While downhill flows are handled by gravity, sewage systems must use lift stations to pump the sewage uphill.  A lift station includes two primary components: (1) a wet well that is an underground basin in which gravity-fed sewage accumulates, and (2) a pump room, which pumps the accumulated sewage in the wet well uphill through a sewer pipe called a force main.  Pump rooms are typically located underground, but are occasionally found above ground.

The pumps in the pump room are activated when the level of sewage in the wet well reaches a certain level, and they turn off when the sewage level drops to a lower level.  While the pumps are off, residual sewage remains in the force main.  During this time, aerobic bacteria continue to digest the sewage and quickly consume the dissolved oxygen contained in the sewage.  The sewage in the force main then becomes anaerobic, which enables anaerobic bacteria to flourish.  Hydrogen sulfide gas is a by-product of the anaerobic bacteria process.

Hydrogen Sulfide (H2S) is the most common odorous gas found in municipal waste water collection and treatment systems.  The gas emits a characteristic odor likened to rotten eggs.  This gas is toxic to humans, and is corrosive to both steel and concrete.  The primary reason sewer systems lose their structural integrity is corrosion.  A primary cause of this corrosion is oxidation of H2S gas on the exposed sewer system surfaces of concrete or metal.  Presently, the use of chemicals is the primary treatment agent.  However, there are growing concerns over problems arising from the residual effects of the increasing use of chemicals in waste water.

AO3’s Answer to the Problem

AO3’s ozone system for the removal and prevention of H2S in sewer force mains is a patented technology.  The use of oxygen and ozone gas is an effective means of controlling H2S if the delivery mechanism is effective.  AO3’s system uses proprietary technology to maximize the benefits of oxygen and ozone gas to eliminate H2S in the force main, which is where most of the H2S is generated in the sewer system.  This technology greatly increases the mass transfer of the oxygen and ozone allowing the gas to remain in suspension longer and thus increase its effectiveness and greatly increasing the efficiency of the system.

The primary mechanisms of action employed by AO3’s system are: (1) Existing H2S in the wet well is oxidized as it enters the force main.  (2) The ozone oxidizes existing sulfides in the wet well as it enters the force main.  Thus, the ozone eliminates the food source for anaerobic bacteria to produce H2S. (3) The ozone is a powerful biocide that reduces the presence and activity of anaerobic bacteria.  (4) The injection of oxygen and ozone changes and maintains the environment of the force main from anaerobic to aerobic.  This aerobic condition limits the number and activity of anaerobic bacteria.  (5) The aerobic environment also enables the aerobic bacteria to flourish and further reduce the waste load in the water before it reaches the treatment plant.  (6) The injection of oxygen and ozone prevents the formation of additional bio-film layer inside the pipe, and even has reduced or eliminated the bio-film inside the pipe.  Controlling the bio-film minimizes the environment for anaerobic bacteria, but also maintains the efficiency of the lift station pumps.

AO3’s ozone system is the only technology currently available that meets all of the following key performance factors that are important to municipalities in deciding upon a treatment method for controlling hydrogen sulfide levels:

  • Treats the primary symptoms of H2S, i.e. odor and corrosion.
  • Eliminates the cause of H2S, i.e. eliminates or significantly reduces the anaerobic bacteria in the force main.
  • Economical cost.
  • Minimal man hours spent in managing the treatment process.
  • Elimination or reduction of chemicals added to the waste stream.
  • Increases dissolved oxygen in force main.
  • Reduces / eliminates bio-film layer in force main.
  • System fits into existing facilities without significant physical modifications.
  • Remote system monitoring and alarm capabilities.

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